The invention concerns a method for operating an internal combustion engine having a plurality of combustion chambers, in the case of which the combustion chambers are charged with fuel and air or with a fuel/air mixture.
The invention also concerns an internal combustion chamber having a plurality of combustion chambers that are capable of being charged with fuel and air or with a fuel/air mixture. Furthermore, the present invention concerns an electronic control unit for an internal combustion engine of this type.
The invention also concerns a memory element for an electronic control unit of an internal combustion engine, in which said memory element a computer program is stored that can be run on a computing element, in particular on a microprocessor. The memory element is developed, in particular, as a read-only memory, a random-access memory, or as a flash memory. Finally, the invention concerns a computer program as well.
The invention concerns multiple-cylinder internal combustion engines with fuel injection, i.e., conventional internal combustion engines with manifold injection as well as direct-injection internal combustion engines having a more modern design. In the case of an internal combustion engine with manifold injection, a fuel/air mixture is produced in an intake manifold of the internal combustion engine and then charged in the combustion chambers of the internal combustion engine. In the case of a direct-injection internal combustion engine, air alone enters the combustion chambers via the intake manifold. Depending on the operating mode of the internal combustion engine, fuel is injected directly into the combustion chambers of the internal combustion engine at different points in time during a power cycle.
With regard for conventional internal combustion engines with manifold injection, it is known from the related art that a specified number of cylinders can be shut down in certain operating states of the internal combustion engine, e.g., in part-load operation or overrun, in order to reduce fuel consumption and exhaust-gas emissions. The cylinders are shut down by halting supply of fuel/air mixture to the cylinders to be shut down. This is accomplished by shutting down intake and/or exhaust valves via which the fuel/air mixture enters the combustion chambers and/or exhaust gases leave the chambers after the fuel/air mixture is combusted. The known method for shutting down cylinders has the disadvantage that only a specified number of cylinders can be shut down. Moreover, sudden torque jumps that are clearly noticeable can occur in certain operating states when the cylinders are shut down or activated.
Direct-injection internal combustion engines can be operated in different operating modes. A distinction is made between stratified-charge operation, which is used with lower loads in particular, and homogeneous operation, in which greater loads are placed on the internal combustion engine. Further operating modes are, e.g., an operating mode for catalytic-converter heating, an operating mode for desulfurization of a catalytic exhaust converter, or for NOx (oxides of nitrogen) regeneration of a catalytic exhaust converter.
In stratified-charge operation, fuel is injected into a combustion chamber during a compression phase in such a fashion that, at the point of ignition, a fuel cloud is located in the immediate vicinity of a spark plug. This injection can take place in different ways. For example, the injected fuel cloud can be located at the spark plug during or immediately after injection, and is ignited by said spark plug. It is also possible that the injected fuel cloud is first directed to the spark plug by means of a motion of the charge, and then ignited. In both of these combustion processes, a stratified charge is present, not uniform fuel distribution.
The advantage of stratified-charge operation lies in the fact that it allows the internal combustion engine to respond to the lower loads being placed on it using a very small amount of fuel. Larger loads cannot be responded to fully using stratified-charge operation.
In homogeneous operation, which is designed to respond to said larger loads, fuel is injected during an intake phase so it can be swirled and, therefore, distributed in the combustion chamber immediately. In this regard, homogeneous operation is similar to the operating method of conventional internal combustion engines with manifold injection. Homogeneous operation can also be used with lower loads, if necessary.
In stratified-charge operation, the throttle valve in the intake manifold leading to the combustion chamber is opened wide, and combustion is controlled via open-loop and/or closed-loop control essentially only by means of the fuel mass to be sprayed. In homogeneous operation, the throttle valve is opened and/or closed depending on the level of torque required, and the fuel mass to be sprayed is controlled via open-loop and/or closed-loop control depending on the inducted air mass.
In both operating modes, i.e., in stratified-charge operation and homogeneous operation, the fuel mass to be sprayed is also governed via open-loop and/or closed-loop control to a value that is optimal in terms of fuel economy, exhaust-gas reduction, and the like, depending on a plurality of further operating variables. Different types of open-loop and/or closed-loop control are used in the two operating modes.
During steady-state operation of a direct-injection internal combustion engine, operating states are possible in which the full level of torque output by the internal combustion engine in the homogeneous operation is not required, even though homogenous operation is requested based on a setpoint torque required by the internal combustion engine, i.e., due to a load being placed on the internal combustion engine. In these cases, due to the relatively rich fuel/air mixture in homogeneous operation (lambda=approx. 1), fuel consumption is relatively high, even though the full level of torque generated in homogeneous operation is not required.
During dynamic operation of the internal combustion engine, i.e., when changing over between operating modes, rapid charge changes in the combustion chambers can result in clearly noticeable, erratic changes in the level of torque output by the internal combustion engine.
The present invention is based on the object of preventing torque jumps during operation of an internal combustion engine in a certain operating state, e.g., when shutting down cylinders or when changing over to a different operating mode.
To attain this object, the invention proposes, based on the method of the type mentioned initially, that the charging of the combustion chambers with fuel and air or with a fuel/air mixture be controlled individually for each combustion chamber via open-loop or closed-loop control.